1. Field of the Invention
The present invention relates to a metal catalyst carrier that is installed in an exhaust system of an internal combustion engine and the like to purify exhaust gas.
2. Description of the Related Art
A conventional metal catalyst carrier is disclosed in Japanese Patent Laid-open Tokkai 2002-143693. This metal catalyst carrier is produced by several manufacturing processes including a preparing process of preparing sheet metals for a corrugated sheet and a flat sheet, a slot forming process of forming the sheet metal for at least the corrugated sheet out of the corrugated sheet and the flat sheet with a plurality of slots, a corrugating process of corrugating one of the metal sheet formed with the slots, a rolling process of stacking the corrugated sheet and the flat sheet and rolling them in multi-layers to obtain a cylindrical core, and a press-fitting process of press-fitting the core into an outer cylinder.
The core, therefore, is provided with a plurality of cell passages, formed between the corrugated sheet and the flat sheet, through which exhaust gas from an engine passes to the atmosphere.
The slots, through which the exhaust gas passes from one to another of the cell passages, constitutes a plurality of slot arrays each of which has the plural slots and is set in a cell passage direction. The slot arrays are arranged to have a predetermined interval equal to zero or larger than zero in a direction perpendicular to the cell passage direction between opening peripheral edge portions of the slots adjacent to each other in the slot arrays adjacent to each other so as not to overlap each other. The above predetermined interval is set to prevent the sheet metal with the slots from being distorted or cracked during the corrugating process.
However, our experiment results have shown that the above condition of the arrangement of the slots is not sufficient for preventing distortions and cracks in the corrugating process of the sheet metal.
Specifically, under the above condition of the arrangement of slots, when an interval in the cell passage direction between the slots adjacent to each in the slot arrays adjacent to each other is less than a predetermined value, the probability that the sheet metal with slots is distorted or cracked in the corrugated process becomes high. Especially when the interval in the direction perpendicular to the cell passage direction is zero, the setting of the interval in the cell passage direction will be another important condition for arranging the slots to avoid the distortions and the cracks.